The CDC won't know the vaccine's effectiveness until clinical trials end in early September, but the agency is confident.

"When we have a virus that's a good match for the vaccine, and we have a good match, vaccines are effective in preventing influenza and effective in preventing the serious consequences that can lead to hospitalization," Skinner said.

Priority Groups

The CDC has also issued vaccination guidelines that give priority to pregnant women; caregivers for children under six months of age; health care and medical workers with direct patient contact; kids six months through four years of age; and children and young adults 5 through 18 with chronic medical conditions such as asthma, heart disease, kidney disease, or diabetes.

"Not only is this group of people at risk for serious complications from influenza, they also serve as spreaders of the flu as well," Skinner said.

One noticeable group is missing from the list—the elderly.

While seasonal flu is especially dangerous for the aged, the H1N1 strain has had a far greater impact on young people under 25 years of age.

Health officials believe that U.S. adults older than 60 may have acquired at least partial immunity to the strain from exposure to previous H1N1 viruses, which circulated in the United States in the first half of the 20th century.

Dodging the Virus

How can you best minimize your chances of catching H1N1? You've likely heard it before: Clean your hands often with soap and water or an alcohol-based hand sanitizer. Try not to touch your mouth or nose, which can spread germs.

To avoid passing the flu along always cover your mouth when you cough or sneeze—you can unknowingly infect others even before your own symptoms appear.

H1N1 sufferers report fever, cough, stuffy nose, sore throat, chills, exhaustion, and headache. Lab tests are the only way to confirm infection with the H1N1 strain and not another type of flu.

If you do get sick, experts urge, stay home for at least 24 hours after your fever is gone.

You won't need to invent an excuse for missed time at work or school. Authorities are urging employers and administrators to develop flexible plans to respond to widespread absenteeism if infections begin in earnest.

With the prospect of a tough flu season ahead, no one knows if the fast-spreading H1N1 will mutate into a far more dangerous form.

Scientists have seen no signs of this so far, but Skinner noted that even routine flu can put people at risk.

"All of the attention that's been given to this new strain really should serve as a reminder of how serious flu season is every year.